This invention relates to a unique receiver system which enhances the directivity of an incoming beam and improves the Signal-to-Noise ratio of received signals, compared to conventional receiver techniques, and which processes stored received data from an antenna to achieve enhanced directivity and improved Signal-to-Noise characteristics. The invention includes a specific antenna configuration interwoven with a special processing scheme. The invention provides dramatic improvement in the performance of a receiving system and affords greater flexibility with respect to several relevant parameters, such as frequency and antenna size and configuration. The invention is beneficial in various applications that utilize receiving systems. Accordingly, the invention is beneficial in a wide range of commercial and military applications. For example, the noise reduction aspect of the invention is applicable to improving the Signal to Noise ratio (S/N) in wired systems as well as in wireless systems. As such, the invention is applicable to a variety of wireless and wireline telecommunications media applications and other wireless systems, including radar.
In typical radar configurations, a common antenna is used for both transmitting and receiving, and the “transmit” and “receive” beams have essentially the same characteristics. In accordance with the present invention, the transmitter beam would not be narrowed and would distribute its power over a solid angle encompassing either a single, or a multiplicity (cluster), of beams. The equivalent power density per narrowed “receive” beam, in accordance with the invention, is the same as in the original beam, but the effective gain of the narrowed receive beam provides overall enhancement.
It is well established that the characteristics of an antenna used in wireless receiving systems are determined largely by the physical size of the antenna measured in wavelengths of the operating frequency of the system. The horizontal and vertical dimensions (in wavelengths) of the antenna aperture determine the “half power width” of the antenna pattern, or “beamwidth”, in each direction. As a consequence, a given available aperture, i.e., “effective antenna” area, dictates the use of shorter wavelengths to obtain proportionately smaller beamwidths and, hence, improvement in directivity of the overall system. Directivity refers to the ability of the receive system to distinguish between signals received from the same general direction. If, for example, the beamwidth of the receive system was narrowed sufficiently, the ability to resolve closely spaced signals would be improved.
The configuration of an antenna can take a variety of geometric forms. For instance, an antenna can be made up of a number of “dipole” radiating elements, each of which receives the signal. A collection of received signals from each element is combined resulting in a final receive signal with a respective overall beamwidth. The beam is then directed, or scanned, in a desired direction to receive signals from, ideally, that particular direction only. As the beam is scanned in other directions, signals from those directions can be distinguished from signals received from the previously scanned directions. However, a problem of interference arises when signals from outside the intended direction of the beam are received and these interference signals cannot be resolved from the signals received from the intended direction. This problem is due mainly to the inability of the given antenna aperture to create a beamwidth narrow enough to distinguish between closely spaced signals.
Further, as each of the individual receive signals is collected from the respective antenna elements, it is typically necessary to amplify the signals to provide sufficient signal strength for subsequent signal processing. Accordingly, in many applications the signal received from each element can be amplified by the use of an associated “preamplifier” having a state-of-the-art “noise figure” to improve the S/N ratio at the beginning, or input, of the system. Under these circumstances, as well as in normal circumstances, this input noise becomes the principal source of noise and establishes the S/N ratio from each element. Enough amplification is typically introduced to provide a signal level appropriate for subsequent processing in the overall system. When the ratio of the signal level as compared to the associated noise level for each receive element is maximized, it becomes easier to distinguish between low-level received signals and the respective noise associated with each received signal. The ability to resolve low-level signals from the noise imparts improved “detectability” and resolution to the overall receive system and is desired in all receive systems.
Therefore, it is desired to raise the S/N ratio as high as possible and at the same time narrow the beamwidth of the antenna in order to distinguish between signals in close proximity from each other and to distinguish signals with low power levels from the noise.